In 1971, at NYU's Steinhardt School of Education (originally known as SEHNAP, School of Education, Health, Nursing, and Arts Professions), he founded a graduate program in media ecology.[2] He became the School of Education's only University Professor in 1993,[2] and was chairman of the Department of Culture and Communication until 2002.

Postman's best known book is Amusing Ourselves to Death (1985), a historical narrative which warns of a decline in the ability of our mass communications media to share serious ideas. Since television images replace the written word, Postman argues that television confounds serious issues by demeaning and undermining political discourse and by turning real, complex issues into superficial images, less about ideas and thoughts and more about entertainment. He also argues that television is not an effective way of providing education, as it provides only top-down information transfer, rather than the interaction that he believes is necessary to maximize learning. He refers to the relationship between information and human response as the Information-action ratio.

He draws on the ideas of media theorist Marshall McLuhan to argue that different media are appropriate for different kinds of knowledge, and describes how cultures value and transfer oral, literate, and televisual information in different ways. He states that 19th century America was the pinnacle of rational argument, an Age of Reason, in which the dominant communication medium was the printed word. During this period, complicated arguments could be transmitted without oversimplification.

Amusing Ourselves to Death was translated into eight languages and sold 200,000 copies worldwide. In addition, it inspired the 1992 album Amused to Death by Roger Waters.

Postman gave a well-known speech at the meeting of the German Society for Computer Science (Gesellschaft für Informatik) on October 11, 1990 in Stuttgart. He argued that our society relies too heavily on information to fix our problems, especially the fundamental problems of human philosophy and survival, that information, ever since the printing press, has become a burden and garbage instead of a rare blessing.

"But what started out as a liberating stream has turned into a deluge of chaos. If I may take my own country as an example, here is what we are faced with: In America, there are 260,000 billboards; 11,520 newspapers; 11,556 periodicals..." "...Everything from telegraphy and photography in the 19th century to the silicon chip in the twentieth has amplified the din of information, until matters have reached such proportions today that for the average person, information no longer has any relation to the solution of problems."

According to his speech, "the tie between information and action has been severed."

"Information is now a commodity that can be bought and sold, or used as a form of entertainment, or worn like a garment to enhance one's status. It comes indiscriminately, directed at no one in particular, disconnected from usefulness; we are glutted with information, drowning in information, have no control over it, don't know what to do with it."

He also compares contemporary society to the Middle Ages, where instead of individuals believing everything told to them by religious leaders, now individuals believe everything told to them by science, making people more naive than in Middle Ages. Individuals in a contemporary society, one that is mediated by technology, could possibly believe in anything and everything, whereas in the Middle Ages the populace believed in the benevolent design they were all part of and there was order to their beliefs.

In his 1992 book Technopoly: the Surrender of Culture to Technology, Postman defines “Technopoly” as a society which believes “the primary, if not the only, goal of human labor and thought is efficiency, that technical calculation is in all respects superior to human judgment ... and that the affairs of citizens are best guided and conducted by experts.” [5]

Postman argues that the United States is the only country to have developed into a technopoly. He claims that the U.S has been inundated with technophiles who do not see the downside of technology. This is dangerous because technophiles want more technology and thus more information.[6] However, according to Postman, it is impossible for a technological innovation to have only a one-sided effect. With the ever-increasing amount of information available Postman argues that: “Information has become a form of garbage, not only incapable of answering the most fundamental human questions but barely useful in providing coherent direction to the solution of even mundane problems.”[7]

In a 1996 interview, Postman re-emphasized his solution for technopoly, which was to give students an education in the history, social effects and psychological biases of technology, so they may become adults who “use technology rather than being used by it”.[8]

Postman has been accused of Ludditism, despite his statement in the conclusion of Amusing Ourselves to Death that "We must not delude ourselves with preposterous notions such as the straight Luddite position."[9]

In this book, Postman asserted that education without a myth or narrative to guide and motivate the student, is education without a purpose. Postman spoke about the function of school being a democracy where different views are shared to help unite us. In Postman's view, multiculturalism is a separatist movement that destroys American unity but on the other hand, he discusses teaching through diversity as an important theme that should be utilized in regard to teaching history, culture and language.

In 1982's The Disappearance of Childhood, Postman argues that what we define as "childhood" is a modern phenomenon. He defines "childhood" as the period from around age 7 – when spoken language is usually mastered – to around age 17 – when written language is mastered. Not coincidentally, these ages correspond to the typical school years.

The word "child" originally meant "son or daughter"; only in modern times did it gain its second meaning – "a person between birth and full growth". Prior to modern times, children were considered "little" adults, rather than today's conception of them as "unformed" adults.

In medieval times, children and adults "lived in the same social and intellectual world" (p. 36). Children dressed the same as adults, shared the same labor and pastimes (gambling was considered a normal childhood pursuit), and with literacy confined to special classes (the monks, for example) had similar intellectual levels. Few children attended school. Children were not shielded from the harsh realities and shameful secrets of the adult world. Adults did not conceal their sexual drives, nor was there a high level of “civilized” mores defining certain behavior, body functions and characteristics as distasteful. "Without a well-developed idea of shame, childhood cannot exist" (9). To Postman, the middle age's absence of literacy, education and shame explains their absence of our conception of childhood.

Postman credits the invention of movable type printing to the idea of childhood. With literacy came adult "secrets,” information available only to adults who could read. And literacy required schools to teach people how to read. "Because school was designed for the preparation of a literate adult, the young became to be perceived not as miniature adults, but as ... unformed adults": (p. 41). These two factors created a new social hierarchy – adults now had "unprecedented control over the symbolic environment of the young" (p. 45). For Postman, 1850–1950 was the "high-water mark of childhood." Children's birthdays began to be celebrated, and their welfare became viewed as something special that needed protection. Children gained specialized clothing and literature – different from adults. Childhood became viewed as an idyllic time of innocence.

In 1950 came television and the disappearance of the child. Television is an egalitarian dispenser of information. No longer were there adult realities and secrets – these were dispensed in news, commercials, and programs to people of any age. Childhood's innocence was lost and the idea of shame became "diluted and demystified" (p. 85). Television, which became the dominant source of information (over books), requires no specialized learning, further diminishing the distinction between children and adults. Some television content adultifies and eroticizes children; some television infantilizes adults. Television has created a three-stage life cycle: infancy, adult-child, and senility (99).

His evidence for the disappearance of childhood: the rise of crime perpetrated by and against children; the increase in sexual activity and drug/alcohol abuse in children; children and adults sharing musical tastes, language, literature, and movies (many big budget movies are comic books that would have been marketed solely to children years ago); the lack of differentiated clothing styles (little girls in high heels, grown men in sneakers). Even childhood games have been replaced by organized sports (Little League, Pee Wee, etc.) which are more like adult sports. "Adulthood has lost much of its authority and aura, and the idea of deference to one who is older has become ridiculous" (p. 133).

He makes a point that civilized behavior acknowledges our animal urges (sex, violence, etc.) but makes them secrets that are kept hidden from children. Since they are no longer secrets, our society may become more barbarian. A case in point is foul language, which is no longer kept hidden from children, and has become more predominant everywhere.

While positing his theory, Postman offers no solution for society on the whole. Even as he wrote in times before the widespread availability of the Internet, he acknowledged that there is probably no turning back from our visual, electronic age. Thus, he writes “Resistance entails conceiving of parenting as an act of rebellion against American culture” (p. 152).

In 1969 and 1970 Postman collaborated with New Rochelle educator Alan Shapiro on the development of a model school based on the principles expressed in Teaching as a Subversive Activity. The result was the "Program for Inquiry, Involvement, and Independent Study" within New Rochelle High School.[10] This "open school" experiment survived for 15 years. In subsequent years many programs following these principles were developed in American high schools, current survivors include the Village School[11] in Great Neck, New York.

In a television interview conducted in 1995 on the MacNeil/Lehrer Hour Postman spoke about his opposition to the use of personal computers in schools. He felt that school was a place to learn together as a cohesive group and that it should not be used for individualized learning. Postman also worried that the personalized computer was going to take away from individuals socializing as citizens and human beings.[12]

^In this speech, Postman encouraged teachers to help their students "distinguish useful talk from bullshit". He argued that it was the most important skill students could learn, and that teaching it would help students understand their own values and beliefs.